This study is a prospective investigation of the biological and contextual correlates of emotional development during middle childhood and the beginning of adolescence in African-American and White children. Over a four-year period, 300 boys and their parents from integrated, working and middle-class communities will be seen yearly. We ask "in what ways do physiological processes and relationships with parents and peers set boys on various trajectories leading to more and less positive emotional functioning?" Aggression (including affective disposition and overt and covert behavior) and behaviors (anxious symptoms and feelings) are the focus of this study. The biological correlates focus on the HPA and HPG axes. The social correlates involve the peer, school, and family contexts. Correlates of development to be considered are: (a) the onset of pubertal processes (increases in FSH secretion, development of secondary sexual characteristics, increases in Testosterone), (b) individual differences in responsivity to stress (using social, cognitive, and physiological challenge tasks), (c) baseline measures of stress (cortisol levels in the early morning, differences between early morning and afternoon levels of cortisol), (d) parent-child interactions (conflict resolution, arousal, parental harshness and firm control) and parental characteristics (temperament and reactivity), (e) family context and environment (single vs. two parent household, neighborhood characteristics), (f) peer relationships (deviant behaviors of peers, rejection, prosocial interactions), and (g) racial discrimination and socialization (for African-American children and parents). While biological and social interactions in development have been a focus of investigations of adolescence and infancy, little prospective research has focused on middle childhood, the time when pubertal processes are initiated and peer and family relationships begin to be redefined.